In recent years, as a window structure for railroad cars that run at high speed, a multi-layered window is known in which an air layer is provided between two transparent panes in order to provide sound insulation and thermal insulation (refer to Patent Document 1). In such a multi-layered window, since the pressure difference between the inside pressure and the outside pressure on the air layer changes greatly, it is supported by a frame material. Furthermore, a sealer, a polymeric coating film, or the like is disposed between the frame material and the multi-layered window in order to make the air layer airtight.
Moreover, in recent years, developments of high speed railroad cars are progressed, and large window panes therefor have become required in order to have good view from the cars. However, there is a problem in that when travelling at high speed in a cold region, breakage and condensation of window panes are likely to occur. For example, if snow attaches beneath a railroad car while travelling in a cold region and the railroad car travels through a tunnel, an updraft is generated and a stone near the track can attach to the snow beneath the railroad car. In this case, a problem can occur in which the stone is lifted up by the updraft and hits the glass window pane, and thereby damaging the glass window pane. To cope with this problem, a technique is used in which a shatterproof film is applied to the outside of the glass window pane. However, it does not completely prevent the glass window pane from being damaged. Therefore, currently, multi-layered windows are widely used in which a glass window pane and a polycarbonate window pane are combined.
Such a multi-layered window has a problem in that although breakage due to stone impact can be prevented by installing a polycarbonate window pane facing the outside of the car, condensation is likely to occur between the glass window pane and the polycarbonate window pane. Especially in a case of a large multi-layered window used in a cold region, since the difference in temperature between the inside and the outside of a car is great, condensation is likely to occur.
In order to solve this, a method is known in which desiccating agent is disposed between a first window pane and a second window pane (refer to Patent Document 2).
As shown in Patent Document 2, between a glass window pane (first window pane) and a polycarbonate window pane (second window pane), a spacer is disposed so as to extend along the edges of the first window pane and the second window pane. Furthermore, a sealer is disposed between the spacer and the first window pane, and between the spacer and the second window pane, such that they are in contact with each other, which unifies the spacer, the first window pane, and the second window pane. By means of such a construction, a sealed air layer is formed between the first window pane and the second window pane. The spacer has a hollow annular shape, and is packed with desiccating agent. Moreover, a plurality of slits is formed in the side wall on the air layer side of the spacer, so that the inside of the spacer and the air layer communicate with each other. As a result, the air layer is dehumidified by the desiccating agent.